Jump to content
MoritzLost

Namespaces, Autoloading and PSR-4: ProcessWire's class loader demystified

Recommended Posts

I've seen a couple of questions regarding namespaces and autoloading floating around the forum recently, so I decided to write a little tutorial. In general, I often see people getting confused when they try to wrap their head around namespaces, autoloading, Composer and the mapping of namespaces to directory structures all at once. In fact, those are very much independent, distinct concept, and it is much easier to explain and understand them separately. So this guide is structured as follows:

  1. How namespaces work in PHP.
  2. How autoloading works in PHP.
  3. Conventions for mapping namespaces to directory structures: PSR-4.
  4. How autoloading works in Composer and ProcessWire's class loader.
  5. How to use the class loader in a ProcessWire module.

Feel free to skip the sections you're already familiar with.

Namespaces in PHP

The purpose of namespaces in PHP is to avoid naming conflicts between classes, functions and constants, especially when you're using external libraries and frameworks. Nothing more. It's important to understand that this has nothing at all to do with autoloading, directory structures or file names. You can put namespaced stuff everywhere you want. You can even have multiple namespaces inside a single file (don't try this at home). Namespaces only exist to be able to use a generic name – for example, ProcessWire's Config class – multiple times in different contexts without getting a naming conflict. Without namespaces, I couldn't use any library that includes a Config class of it's own, because that name is already taken. With namespaces, you can have a distinction between the classes ProcessWire\Config and MoritzLost\Config. You can also use sub-namespaces to further segregate your code into logical groups. For example, I can have two classes MoritzLost\Frontend\Config and MoritzLost\Backend\Config– a class name only needs to be unique within it's namespace.

You can declare the namespace for a PHP file using the namespace statement at the top:

// file-one.php
<?php
namespace ProcessWire;

// file-two.php
<?php
namespace MoritzLost\Frontend;

This way, all classes, methods and constants defined inside this file are placed in that namespace. All ProcessWire classes live in the ProcessWire namespace.

Now to use one of those classes – for example, to instantiate it – you have a couple of options. You can either use it's fully qualified class name or import it into the current namespace. Also, if you are inside a namespaced file, any reference to a class is relative to that namespace. Unless it starts with a backward slash, in this case it's relative to the global namespace. So all of those examples are equivalent:

// example-one.php
<?php
namespace ProcessWire;
$page = new Page();

// example-two.php
<?php
use ProcessWire\Page;
$page = new Page();

// example-three.php
<?php
$page = new ProcessWire\Page();

// example-four.php
<?php
namespace MoritzLost\Somewhere\Over\The\Rainbow;
$page = new \ProcessWire\Page();

The use statement in the second example can be read like this: “Inside this file, all references to Page refer to the class \ProcessWire\Page

How autoloading works

Every PHP program starts with one entry file – for ProcessWire, that's usually it's index.php. But you don't want to keep all your code in one file, that would get out of hand quickly. Once you start to split your code into several individual files however, you have to take care of manually including them with require or include calls. That becomes very tedious as well. The purpose of autoloading is to be able to add new code in new files without having to import them manually. This, again, has nothing to do with namespaces, not even something with file locations. Autoloading is a pretty simple concept: If you try to use a class that hasn't been loaded yet, PHP calls upon it's registered autoloaders as a last-ditch attempt to load them before throwing an exception.

Let's look at a simple example:

// classes.php
<?php
class A { /** class stuff */ }
class B { /** class stuff */ }

// index.php
<?php
spl_autoload_register(function ($class) {
    include_once 'classes.php';
});
new A();
new B();

This is a complete and functional autoloader. If you don't believe me, go ahead and save those two files (classes.php and index.php) and run the index.php with php -f index.php. Then comment out the include_once call and run it again, then you'll get an error that class A was not found.

Now here's what happens when index.php is executed (with the autoloader active):

  1. Our anonymous function is added to the autoload queue through spl_autoload_register.
  2. PHP tries to instantiate class A, but can't because it's not loaded yet.
  3. If there was no autoloader registered, the program would die with a fatal error at this point. But since there is an autoloader ...
  4. The autoloader is called. Our autoloader includes classes.php with the class definition.
  5. That was a close one! Since the class has been loaded, execution goes back to the index.php which can now proceed to instantiate A and B. If the class was still not loaded at this point, PHP would go back to the original plan and die.

One thing to note is that the autoloader will only be called once in this example. That's because both A and B are in the same file and that file is included during the first call to the autoloader. Autoloading works on files, not on classes!

The important takeaway is that PHP doesn't know if the autoloader knows where to find the class it asks for or, if there are multiple autoloader, which one can load it. PHP just calls each registered autoloader in turn and checks if the class has been loaded after each one. If the class still isn't loaded after the last autoloader is done, it's error time.

What the autoloader actually does is pretty much wild wild west as well. It takes the name of the class PHP is trying to load as an argument, but it doesn't have to do anything with it. Our autoloader ignores it entirely. Instead, it just includes classes.php and says to itself “My job here is done”. If class A was in another file, it wouldn't have worked.

This process has two main advantages:

  1. Since autoloaders are only called on-demand to load classes just in time, we only include the files we actually need. If in the example above class A and B are not used in some scenarios, the classes.php will not be included, which will result in better performance for larger projects (though this isn't as cut and dry, since autoloading has it's own overhead, so if you load most classes anyway during a single request, it will actually be less efficient).
  2. If the autoloader is smart enough to somehow map class names to the files they're located in, we can just let the autoloader handle including the classes we need, without having to worry about jamming include statements everywhere. That brings us to ...

PSR-4, namespaces and directory structures

As you see, namespaces and autoloading are both pretty limited concepts. And they aren't inherently linked to each other. You can namespace your classes without ever adding an autoloader, and you can autoload classes that are all in the same namespace. But they become useful when you put them together. At the core of all that autoloading talk is a simple idea: By putting classes in files named after their class names, and putting those files in directory hierarchies based on the namespace hierarchy, the autoloader can efficiently find and load those files based on the namespace. All it needs is a list of root namespaces with their corresponding directories.

The exact way class names and namespaces are mapped to directory structures and file names is purely conventional. The accepted convention for this is PSR-4. This is a super simple standard which basically just sums up the ideas above:

  1. A base namespace is mapped to a specific directory in the file system. When the autoloader is asked to load a class in that namespace (or a sub-namespace of it), it starts looking in that folder. This "base" namespace may include multiple parts – for example, I could use MoritzLost\MyAwesomeLibrary as a base and map that to my source directory. PSR-4 calls this a "namespace prefix".
  2. Each sub-namespace corresponds to a sub-directory. So by looking at the namespace, you can follow subdirectories to the location where you expect to find the class file.
  3. Finally, the class name is mapped directly to the file name. So MyCoolClass needs to be put inside MyCoolClass.php.

This all sounds simple and straightforward - and it absolutely is! It's only once you mash everything together, mix up language features, accepted conventions and proprietary implementations like Composer on top that it becomes hard to grasp in one go.

Composer and ProcessWire's class loader

Now all that's left is to talk about how Composer and ProcessWire provide autoloading.

Composer, of course, is primarily a tool for dependency management. But because most libraries use namespaces and most developers want to have the libraries they're using autoloaded, those topics become a prerequisite to understanding what Composer does in this regard. Composer can use different autoloading mechanisms; for example, you can just give it a static list of files to include for every request, or use the older PSR-0 standard. But most modern libraries use PSR-4 to autoload classes. So all Composer needs to function is a mapping of namespace prefixes to directories. Each library maintains this mapping for it's PSR-4-structured classes through the autoload information in their composer.json. You can do this for your own site to: Just include the autoload information as shown in the documentation and point it to the directory of your class files.

Composer collects all that information and uses it to generate a custom file at vendor/autoload.php — that's the one you need to include somewhere whenever you set up Composer in one of your projects. Bells and whistles aside, this file just registers an autoloader function that will use all the information collected from your own and your included libraries' composer.json to locate and include class files on demand.

You can read more about how to optimize Composer's autoloader for production usage here. If you want to read up on how to set up Composer for your own sites, read my ProcessWire + Composer integration guide instead.

And finally, what does ProcessWire do to handle all this? Turns out, ProcessWire has it's own autoloader implementation that is more or less PSR-4 compliant. You can access it as an API variable ($classLoader or wire('classLoader'), depending on context). Instead of using a static configuration file like Composer, the namespace -> directory mapping is added during the runtime by calling $classLoader->addNamespace. As you would expect, this function accepts a namespace and a directory path. You can use this to register your own custom namespaces. Alternatively, if you have site-specific classes within the ProcessWire namespace, you can just add their location to the class loader using the same method: $classLoader->addNamespace('ProcessWire', '/path/to/your/classes/').

Utilizing custom namespaces and autoloading in ProcessWire modules

Now as a final remark, I wanted to give an example of how to use custom namespaces and the class loader in your own modules. I'll use my TrelloWire module as an example:

  1. Decide what namespace you're going to use. The main module file should live in the ProcessWire namespace, but if you have other classes in your module, they can and should use a custom namespace to avoid collisions with other modules. TrelloWire uses ProcessWire\TrelloWire, but you can also use something outside the ProcessWire namespace.
  2. You need to make sure to add the namespace to the class loader as early as possible. If either you or a user of your module tries to instantiate one of your custom classes before that, it will fail. Good places to start are the constructor of your main module file, or their init or ready methods.

Here's a complete example. The module uses only one custom namespaced class: ProcessWire\TrelloWire\TrelloWireApi, located in the src/ directory of the module. But with this setup, I can add more classes whenever I need without having to modify anything else.

/**
 * The constructor registers the TrelloWire namespace used by this module.
 */
public function __construct()
{
    $namespace = 'ProcessWire\\TrelloWire';
    $classLoader = $this->wire('classLoader');
    if (!$classLoader->hasNamespace($namespace)) {
        $srcPath = $this->wire('config')->paths->get($this) . 'src/';
        $classLoader->addNamespace($namespace, $srcPath);
    }
}

Source

Thanks for making it through to the very end! I gotta learn to keep those things short. Anyway, I hope this clears up some questions about namespaces and autoloading. Let me know if I got something wrong, and feel free to add your own tips and tricks!

  • Like 21
  • Thanks 9

Share this post


Link to post
Share on other sites

Great read! Perfectly laid out! A ready Medium article in a post! And maybe it should be published elsewhere, as it provides a lot of useful info not only for PW devs (and would bring some attention to PW).

  • Like 3

Share this post


Link to post
Share on other sites
On 5/16/2020 at 8:52 PM, Ivan Gretsky said:

Great read! Perfectly laid out! A ready Medium article in a post! And maybe it should be published elsewhere, as it provides a lot of useful info not only for PW devs (and would bring some attention to PW).

Thanks! I'm not sure this needs to be posted anywhere else – there's already a lot of information on those topics out there. I primarily wrote this to (1) present all that information in a ProcessWire context, using ProcessWire modules and the class loader as examples and (2) to have it as a resource I can link to when questions regarding those topics come up. But maybe I should cross-post this to Medium for some ProcessWire exposure, there's a lot of useless stuff there anyway 😆

  • Like 2

Share this post


Link to post
Share on other sites

Lots of useless stuff on Wordpress, coronavirus, and motivating yourself to effectively deal with those, but not enough on ProcessWire))

  • Like 1
  • Haha 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By MrSnoozles
      Hey everyone,
      I was just wondering what is the purpose of autoloading the file wire/core/ProcessWire.php in composer.json? As far as I can see that file gets required again anyway in index.php, around line 32.

      For me this line has no purpose but one major drawback: When requiring ProcessWire as dependecy in a module (e.g. to write tests against a clean ProcessWire installation), an error is thrown that the class is already in use.
      Fatal error: Cannot declare class ProcessWire\ProcessWire, because the name is already in use
       
      Does this autoloading have any purpose?
    • By Ivan Gretsky
      Most of us know and use site/config-dev.php file. If present, it is used instead of site/config.php, so it is easy to set database connection and debug mode for local development, not touching the production config. It is also very useful when working with git. You can simply ignore it in the .gitignore file, so local settings won’t end up in the repo.
      But sometimes you need to add code to site/ready.php or site/init.php just for the dev environment. For example, to add ryan’s super cool on demand images mirrorer. I can’t live without it when working with big sites, which have more assets then I want to download to my desktop.
      It would be great if there was something like site/ready-dev.php for this. Not out-of-the-box, but it’s pretty easy to achieve. Unlike site/config-dev.php, site/ready.php is not hardcoded. It’s name is set with a special config setting:
      // wire/config.php $config->statusFiles = array( 'boot' => '', 'initBefore' => '', 'init' => 'init.php', 'readyBefore' => '', 'ready' => 'ready.php', 'readySite' => '', 'readyAdmin' => '', 'render' => '', 'download' => '', 'finished' => 'finished.php', 'failed' => '', ); As you can see, we can not only define, which files are loaded on init, ready and finished runtime states, but probably even add more if we need to.
      So we override this setting in site/config-dev.php like this:
      // site/config-dev.php // Change ready.php to ready-dev.php $temp = $config->statusFiles; $temp['ready'] = 'ready-dev.php'; $config->statusFiles = $temp; For some reason we can’t just do
      $config->statusFiles['ready'] = 'ready-dev.php'; and have to override the whole array. Maybe you PHP gurus can explain this in the comments.
      Now we can create the site/ready-dev.php file and place all the dev-only code there. Important thing is to include the main site/ready.php.
      // site/ready-dev.php include 'ready.php'; // DEV HOOK TO MIRROR ASSETS ON DEMAND $wire->addHookAfter('Pagefile::url, Pagefile::filename', function($event) { $config = $event->wire('config'); $file = $event->return; if($event->method == 'url') { // convert url to disk path $file = $config->paths->root . substr($file, strlen($config->urls->root)); } if(!file_exists($file)) { // download file from source if it doesn't exist here $src = 'https://mysite.com/site/assets/files/'; $url = str_replace($config->paths->files, $src, $file); $http = new WireHttp(); try { $http->download($url, $file); } catch (\Exception $e) { bd($file, "Missing file"); } } }); Do not forget to replace "mysite.com" if you’re copypasting this))
      Now, add the newly created file to the `.gitignore` and we’re done.
       
      # .gitignore # Ignore dev files site/config-dev.php site/ready-dev.php Thanks for reading!
       
    • By horst
      Change Default Language to be None-English | Walk Trough
      When you start a new (single) language site and the default language shouldn't be English, you can change it this way:
      Go to the modules core section:

       
      Select the Language ones by the filter function:

       
      We have four language related modules here, but for a single language site in none english,
      we only need the base module, named "Languages Support". So go on and install it.

       
      After that, you can leave it, ... 

       
      ... and switch to the newly created Language section under SETUP:

       
      Select the default language

       
      Enter your new language name or its Shortcut and save the page.
      I will use DE for a single language site in german here as example:

       
      Now I go to the ProcessWire online modules directory, down to the subsection for language packs and select
      and download my desired (german) one: 

       

       

       

       
      After downloading a lang pack as ZIP, I go back into my SETUP > LANGUAGES > default language page in admin,
      select the downloaded lang pack ZIP and install it:

       

       

       
       
      After the ZIP is uploaded, the files are extracted and installed, most of my screen is already in
      the new default language. To get all fully switched, we save and leave that page, ...

       
      ... and completely logout from the admin.

       
      Now, of course, we directly login back, ...

      ... and see, that now also the cached parts of the admin have switched to the new default language. 🙂

       
      That was it for a single language site in none english.
       
      If you want to have a multi language site, just add more languages to the SETUP > LANGUAGES section.
      When using a multi language site, I think you also want to use multi language input fields, and maybe different page names for your language page pendents. If so, you need to go into MODULES > CORE > filter LANGUAGE and install what you need or want to use of it, (if not already done).
      Thanks for reading and happy coding, 🙂
       
    • By MoritzLost
      I've been working with ProcessWire for a while now, and I've noticed that using Composer to manage dependencies and autoload external libraries isn't as prevalent in ProcessWire development as in other areas of PHP programming. I started out by using the default setup recommend in this blogpost. However, one major problem I have with this approach is that all external dependencies live in the webroot (the directory the server points to), which is unfavourable from a security standpoint and, in my opinion, just feels a bit messy.
      In this tutorial, I want to go through a quick setup of Composer and ProcessWire that keeps the dependencies, all custom-written code and other source material outside of the webroot, and makes full usage of the Composer autoloader. This setup is pretty basic, so this tutorial is probably more useful to beginners (this is why I'll also include some general information on Composer), but hopefully everyone can take something away from this for their personal workflow.
      Site structure after setup
      This is what the directory structure can look like after the setup:
      . ├── composer.json ├── composer.lock ├── node_modules │   └── ... ├── public │   ├── index.php │   ├── site │   ├── wire │   └── ... ├── packacke-lock.json ├── package.json ├── sass │   ├── main.scss │   ├── _variables.scss │   └── ... ├── src │   ├── ContentBag.php │   └── ... └── vendor ├── autoload.php ├── composer ├── league ├── symfony └── ... As mentioned, the main point of this setup is to keep all external libraries, all other custom source code and resources out of the webroot. That includes Composer's vendor folder, your node_modules and JavaScript source folder if you are compiling JavaScript with webpack or something similar and including external scripts via NPM, or your CSS preprocessor files if you are using SASS or LESS. In this setup, the public directory acts as the webroot (the directory that is used as the entry point by the server, DocumentRoot in the Apache configuration). So all other files and directories in the mysite folder aren't accessible over the web, even if something goes wrong.
      One caveat of this setup is that it's not possible to install ProcessWire modules through Composer using the PW Module Installer (see Blogpost above), but that's just a minor inconvenience in my experience.
      Installation
      You'll need to have composer installed on your system for this. Installation guides can be found on getcomposer.org.
      First, open up your shell and navigate to the mysite folder.
      $ cd /path/to/mysite/ Now, we'll initialize a new Composer project:
      $ composer init The CLI will ask some questions about your projects. Some hints if you are unsure how to answer the prompts:
      Package names are in the format <vendor>/<project>, where vendor is your developer handle. I use my Github account, so I'll put moritzlost/mysite (all lowercase). Project type is project if you are creating a website. Author should be in the format Name <email>. Minimum Stability: I prefer stable, this way you only get stable versions of dependencies. License will be proprietary unless you plan on sharing your code under a FOSS license. Answer no to the interactive dependencies prompts. This creates the composer.json file, which will be used to keep track of your dependencies. For now, you only need to run the composer install command to initialize the vendor directory and the autoloader:
      $ composer install Now it's time to download and install ProcessWire into the public directory:
      $ git clone https://github.com/processwire/processwire public If you don't use git, you can also download ProcessWire manually. I like to clean up the directory after that:
      $ cd public $ rm -r .git .gitattributes .gitignore CONTRIBUTING.md LICENSE.TXT README.md Now, setup your development server to point to the /path/to/mysite/public/ directory (mind the public/ at the end!) and install ProcessWire normally.
      Including & using the autoloader
      With ProcessWire installed, we need to include the composer autoloader. If you check ProcessWire's index.php file, you'll see that it tries to include the autoloader if present. However, this assumes the vendor folder is inside the webroot, so it won't work in our case.
      One good place to include the autoloader is using a site hook file. We need the autoloader as early as possible, so we'll use init.php:
      EDIT: As @horst pointed out, it's much better to put this code inside the config.php file instead, as the autoloader will be included much earlier:
      // public/site/config.php <?php namespace Processwire; require '../../vendor/autoload.php'; The following also doesn't apply when including the autoloader in the config-file.
      This has one caveat: Since this file is executed by ProcessWire after all modules had their init methods called, the autoloader will not be available in those. I haven't come across a case where I needed it this early so far; however, if you really need to include the autoloader earlier than that, you could just edit the lines in the index.php file linked above to include the correct autoloader path. In this case, make sure not to overwrite this when you update the core!
      Now we can finally include external libraries and use them in our code without hassle! I'll give you an example. For one project, I needed to parse URLs and check some properties of the path, host et c. I could use parse_url, however that has a couple of downsides (specifically, it doesn't throw exceptions, but just fails silently). Since I didn't want to write a huge error-prone regex myself, I looked for a package that would help me out. I decided to use this URI parser, since it's included in the PHP League directory, which generally stands for high quality.
      First, install the dependency (from the project root, the folder your composer.json file lives in):
      $ composer require league/uri-parser This will download the package into your vendor directory and refresh the autoloader.
      Now you can just use the package in your own code, and composer will autoload the required class files:
      // public/site/templates/basic-page.php <?php namespace Processwire; use \League\Uri\Parser; // ... if ($url = $page->get('url')) { $parser = new Parser(); $parsed_url = $parser->parse($url); // do stuff with $parsed_url ... } Wiring up custom classes and code
      Another topic that I find really useful but often gets overlooked in Composer tutorials is the ability to wire up your own namespace to a folder. So if you want to write some object-oriented code outside of your template files, this gives you an easy way to autoload those using Composer as well. If you look at the tree above, you'll see there's a src/ directory inside the project root, and a ContentBag.php file inside. I want to connect classes in this directory with a custom namespace to be able to have them autoloaded when I use them in my templates.
      To do this, you need to edit your composer.json file:
      { "name": "moritzlost/mysite", "type": "project", "license": "proprietary", "authors": [ { "name": "Moritz L'Hoest", "email": "info@herebedragons.world" } ], "minimum-stability": "stable", "require": {}, "autoload": { "psr-4": { "MoritzLost\\MySite\\": "src/" } } } Most of this stuff was added during initialization, for now take note of the autoload information. The syntax is a bit tricky, since you have to escape the namespace seperator (backslash) with another backslash (see the documentation for more information). Also note the PSR-4 key, since that's the standard I use to namespace my classes.
      The line "MoritzLost\\MySite\\": "src/" tells Composer to look for classes under the namespace \MoritzLost\MySite\ in the src/ directory in my project root. After adding the autoload information, you have to tell composer to refresh the autoloader information:
      $ composer dump-autoload Now I'm ready to use my classes in my templates. So, if I have this file:
      // src/ContentBag.php <?php namespace MoritzLost\MySite; class ContentBag { // class stuff } I can now use the ContentBag class freely in my templates without having to include those files manually:
      // public/site/templates/home.php <?php namespace Processwire; use MoritzLost\MySite\ContentBag; $contentbag = new ContentBag(); // do stuff with contentbag ... Awesome!
      By the way, in PSR-4, sub-namespaces correspond to folders, so I can put the class MoritzLost\MySite\Stuff\SomeStuff in src/Stuff/SomeStuff.php and it will get autoloaded as well. If you have a lot of classes, you can group them this way.
      Conclusion
      With this setup, you are following secure practices and have much flexibility over what you want to include in your project. For example, you can just as well initialize a JavaScript project by typing npm init in the project root. You can also start tracking the source code of your project inside your src/ directory independently of the ProcessWire installation. All in all, you have good seperation of concerns between ProcessWire, external dependencies, your templates and your OOP-code, as well as another level of security should your Server or CGI-handler ever go AWOL. You can also build upon this approach. For example, it's good practice to keep credentials for your database outside the webroot. So you could modify the public/site/config.php file to include a config or .env file in your project root and read the database credentials from there.
      Anyway, that's the setup I came up with. I'm sure it's not perfect yet; also this tutorial is probably missing some information or isn't detailed enough in some areas depending on your level of experience. Feel free to ask for clarification, and to point out the things I got wrong. I like to learn as well 🙂
      Thanks for making it all the way to the bottom. Cheers!
×
×
  • Create New...